Echo components in a hybrid circuit are generated by a reception signal flowing into a transmission signal path through the hybrid circuit. An echo canceller cancels the echo components, thereby preventing degradation in voice quality due to the echo components. The echo components arise when the reception signal is a voice signal, but they also arise when the reception signal is a tone signal.
A conventional echo canceller which avoids false convergence resulting from presence of a tone signal is disclosed in, for example, Patent Document 1.
Patent Document 1 is Japanese Patent Application Kokai (Laid Open) Publication No. 2005-110307.